Yes you can easily change the text displayed in the subscription widget.
PRO TIP: For international stores not using English, you can use this to replace the text with your language.
Legacy Themes (not 2.0):
Step 1: From Ongoing, click Settings and then Subscription Widget
Step 2: Type in your new custom text. You can replace the text to say whatever you would like it to display
Step 3: Click Save
2.0 Themes (such as Dawn):
From Shopify Admin, under Online Sales click on Themes
Click Customize on your Live Theme.
From the drop down menu click on Product, then Default Product.
In the Product Information section, click on Subscription Plans (this is the Ongoing app "block")
In the left hand-side of the screen you can type in your new custom text in the text fields, and click Save.